Ground compacting apparatus

ABSTRACT

A method and apparatus for controlling the frequency of vibration of a vibratory compactor having a vibration producing means and a ground compaction member. The frequency of vibration of the compactor is varied to obtain approximately maximum compacting efficiency by varying the speed of cyclic movement of the vibration producing means in accordance with a detected phase relationship between the cyclic movement of the vibration producing means and the cyclic movement of the ground compacting member.

ilnited States Patent [191 Harris Mar. 19, 1974 1 GROUND COMPACTING APPARATUS 2.897,734 8/1959 Bodine 404/75 [75] Inventor: Jesse W. Harris, San Antonio, Tex. FOREIGN PATENTS OR APPLICATIONS 822.979 11/1951 Germany Assignee: Tampo Manufacturing Company,

San Antonio, Tex.

Filed: May 23, 1972 Appl. No.: 256,195

Related US. Application Data [63] Continuation of Ser. No. 84.400. Oct. 27. 1970.

abandoned.

[52] US. Cl. 404/117, 404/103 [51] Int. Cl. E016 19/28 [58] Field of Search 404/103, 117

[56] References Cited 7 UNITED STATES PATENTS 3.411.420 11/1968 Martin 404/117 3.599.543 8/1971 Kerridge 404/117 3.605.583 9/1971 Keppler 404/117 3.053.157 9/1962 Martin 404/117 Primary ExaminerRoy D. Frazier Assistant Examiner--Thomas J. Holko Attorney. Agent, or FirmBurns. Doane. Swecker &

Mathis [5 7] ABSTRACT A method and apparatus for controlling the frequency of vibration of a vibratory compactor having a vibration producing means and a ground compaction member; The frequency of vibration of the compactor is varied to obtain approximately maximum compacting efficiency by varying the speed of cyclic movement of the vibration producing means in accordance with a detected phase relationship between the cyclic movement of the vibration producing means and the cyclic movement of the ground compacting member.

23 Claims, 16 Drawing Figures PATENTEDHAR 19 I974 SHEU 1 OF 9 INVENTOR JESSE W. HARRIS ATTORNEYS PAIENIEU m 1 9 I874 3; T 97 L 9 54 sum 2 or 9 (ECCENT RIC MEANS) DOWN (DETEQOR 90) A JL up v H04 (ROLLER REST REST VIBRATION) DOWN DOWN (DETEQOR 72) A w A t k PATENTEDMAR 19 m4 3.797.954

SHEET 3 OF 9 INVENTOR JESSE w. HARRIS PATENTED MAR 1 9 I974 SHEET B []F 9 INVENTOR JESSE W. HARRIS ATTORNEYS PATENTEUHAR 19 I974 SHEET 5 0F 9 INVENTOR JESSE Wv HARRIS BY Ewns am swea' ATTORNEYS PATENTEDHAR 19 1914 SHEET 6 0F 9 wot C 51 gamma 3 C Q ANN @2858 Q 5:2: Ex 5: m

PATENTEDHAR 19 m4 SHEET 8 OF 9 F IGIO INVENTOR JESSE W. HARRlS BY 50M; gem M a M ATTQRNEYS GROUND coMPAcrrNo APPARATUS This is a continuation, division of application Ser. No. 34,400, filed Oct. 27, 1970 now abandoned.

BACKGROUND OF THE INVENTION This invention relates to a vibratory compactor for compacting earth, roads and the like, and it relates more specifically to apparatus for controlling the frequency of movement of the vibration producing element of a vibratory compactor to achieve enhanced compaction efficiency.

Various types of earth or road compacting machines employing vibrating ground engaging members have been employed heretofore. For example, one such machine includes a rotatable roller which moves along the ground as the machine traverses the surface being compacted and which is vibrated up and down by driven eccentric means suitably associated with the roller. The speed of the eccentric means is adjustable independently of the speed of traversing movement so that the frequency of roller vibration may be altered as desired in the light of the particular compaction operation being performed.

Ordinarily, greatest compaction efficiency is realized if the frequency of the vibration producing means (e.g. the speed of the eccentrics in machines of the type referred to above) is made to correspond with the natural frequency of the vibrated system made up of the material being compacted and the compacting member. However, practical difficulties have been encountered in obtaining and maintaining the desired correlation between the frequency of the vibration producing means and the natural frequency of the system vibrated thereby; As the compacting machine traverses the surface being compacted, it moves over materials having different characteristics and the natural frequency of vibrating system changes. Hence, changes in the frequency of the vibration producing means must be made in order to achieve resonance.

Since the desired resonance conditions ordinarily are manifested by maximization of the amplitude of the movements of the ground engaging compacting member, it has been proposed in the past that means be provided for measuring on a continuing basis this amplitude quantity and displaying such information at a location where it might be observed and acted upon by the operator of the machine. See in this connection Martin U.S. Pat. No. 3,053,157, disclosing a system in which information concerning the amplitude of vibratory roller vibration is displayed on a meter adjacent the operator's station and the operator manually adjusts the speed of rotatable eccentric means from time to time in an effort to obtain the desired results.

This technique, while desirable in result from the standpoint of intended enhancement of compaction efficiency, may be improved upon from various operational standpoints.

For example, this technique necessarily relies upon a trial and error approach. The vibrator amplitude reading available to the operator at any particular moment does not provide a definite indication of whether the frequency of the driven vibration producing means corresponds to the natural frequency of the system being vibrated thereby. An amplitude value measured when compacting one type of soil with maximum efficiency might well be the same numerically as an amplitude value characteristic of inefficientcompaction of some other soil. Hence, it becomes necessary for the operator to initiate vibratory frequency changes from time to time to test whether such changes have an effect of increasing vibrator amplitude.

Moreover, even where the operator senses that a change may be desirable, the amplitude reading available at that moment does not indicate the direction of change which should be explored. It is up to the operator to make changes in both directions, correlate the effects produced by such changes, and then select the vibration frequency best suited for the particular conditions under consideration. Moreover, such evaluations may soon lose their utility if the machine moves on to compact surface materials of different density, etc.

OBJECTS AND SUMMARY OF A PREFERRED FORM OF THE INVENTION It is therefore a general object of the present invention to provide novel methods and apparatus for enhancing the compaction efficiency of a vibratory compactor.

It is a particular object of the present invention to provide such novel method and apparatus wherein the desirability of making a change in the speed of the vibration producing means may be determined without the need for evaluating the effects produced by experimental increases or decreases in speed.

It is yet another object of the present invention to provide a novel method and apparatus for automatically controlling the speed of a vibration producing means in a vibratory compactor in relation to the phase difference between the movement of the vibration pro-' ducing means and certain vibrating parts of the compactor, without the need for measuring the amplitude of vibration of the ground engaging compacting member.

A preferred form of the present invention intended to accomplish the above objects includes a frame, a ground engaging compacting member resiliently mounted on the frame, a vibration producing means movable at selectively variable speeds (frequencies) for vibrating the compacting member, means for detecting the phase relationship between the movement of the vibration producing means and the forced vibration of selected vibrating parts of the compactor, and means for varying the speed of the vibration producing member in relation to the detected phase relationship.

Greatest compaction efficiency ordinarily is obtainable under conditions of resonance between the vibration inducing forces and the system being vibrated. The existence of such conditions may be detected in accordance with the invention, because they are manifested by a phase difference between the vibration producing means and the vibrated ground contacting member.

For example, in the eccentric motivated vibratory roller unit referred to above, the eccentric will lead the roller by 90 under conditions of resonance. If the measured phase difference between the eccentric movement and the roller vibrations is less than 90, this indicates that the eccentric speed is less than that required for resonance.

Hence, practically instantaneous phase difference measurements provide an amplitude insensitive control parameter which may be monitored on a continuing basis and which may be relied upon not only to indicate needs for eccentric speed adjustments but also the direction in which such adjustments should be made in order to produce desired effects.

The automatic systems of this invention accomplish such monitoring and make whatever changes in the speed of the vibration producing means which may be required to maintain the phase difference within a preselected range. Typically, the preselected range will center on a 90 phase difference, so as to yield conditions approximating resonance, but center points deviating by predetermined amounts from 90 may be selected for some types of operations. The size of the range also is subject to variation to meet particular needs. A partically useful approximation of resonant conditions ordinarily can be achieved for example by so regulating the speed of the eccentric that the eccentric mass leads the ground contacting roller by an angle of from about 75 to about 105.

A more complete understanding of these and other features of the present invention will be gained from a consideration of the following detailed description of certain preferred forms of the. invention illustrated in the accompanying drawings, wherein like numerical designations have been utilized to identify like elements.

THE DRAWINGS FIG. 1 is a schematic plan view of a self-propelled vibratory compacting machine embodying one preferred form of the present invention.

FIG. 2 is a mechanical diagram of an arrangement for regulating the speed of the eccentric means of the machine of FIG. 1.

FIG. 3 is a partial cross-sectional view of portion of the compacting machine of FIG. 1 taken along the line 3-3 showing detector means in position on the machine components.

FIG. 4 is a graphical representation of the movement of the vibration producing means and the ground .engaging compacting member of the compacting machine of FIG. 1 together with a graphical representation of electrical signals'related thereto.

FIG. 5 is an electrical schematical diagram of the control system for the embodiment of FIGS. 1-3.

FIG. 6 is a cross-sectional and schematic view, similar to that of FIG. 5, showing another form of the movement detectors according to the present invention.

FIG. 7 is a schematic representation of the eccentric means movement detecting means of FIG. 6.

FIG. 8 is a graphical illustration of the operation of the movement detecting means of FIG. 6.

FIG. 9 is a schematic diagram of a preferred form of a control system utilized in connection with the movement detecting means of FIG. 6.

FIG. 10 is a schematic representation of yet another form of an eccentric means movement detecting means suitable for use with the compacting machine of FIG. 1.

FIG. 11 is a graphical illustration of the operation of the detecting means of FIG. 10.

FIG. 12 is another form of a vibration detecting means suitable. for use with the compacting machine of FIG. 1.

FIG. 13 is a schematic diagram of a control system utilized in connection with the movement detecting means of FIGS. 10 and 12.

I form of movement detecting means suitable for use with the compacting machine of FIG. 1.

FIG. 16 is a schematic diagram of a control system utilized in connection with the detecting means of FIGS. 14 and 15.

DETAILED DESCRIPTION A vibratory compacting machine embodying the present invention is shown in FIG. 1.

The machine includes a tractor frame 10 supported for ground traversing movement on spaced parallel wheels 12 and 14 which may be driven by a suitable propelling means such as a hydrostatic drive comprising a pump unit 15 and a motor unit l6.

A roller support frame 18 is pivotally attached to the forward end of the tractor frame 10 for movement about a generally vertical axis 20. The roller support frame 18 resiliently supports a freely rotatable, ground engaging roller 22 which functions as a ground compacting member, the term ground meaning the surface to be compacted, e.g. asphalt, earth, or other such surfaces.

Located within the roller 22 and mounted for independent rotation with respect thereto is rotatable eccentric means schematically illustrated at 24. The eccentric means 24 functions to vibrate the roller 22 and may be of any suitable type.

A drive motor 26 for rotating the eccentric means 24 may be mounted on the roller support frame 18 in any suitable manner. This motor 26 may, for example, be

a conventional hydraulic motor and may be hydraulically coupled, by way of a hose assembly 30, to a pump 28 mounted on the tractor frame 10 and driven by the engine 17. The illustrated motor 26 and the pump 28 together preferably comprise the reversible, variable speed, hydrostatic transmission of the type disclosed in U.S. Pat. No. 3,605,583 of.I.E. Keppler (the disclosure of which is hereby incorporated by reference), assigned to the assignee of the present invention. This type of hydrostatic transmission permits infinitely variable and rapid speed control of the eccentric means 24.

As also disclosed in the 'Keppler U.S. Pat. No. 3,605,583, it is desirable that the direction'of rotation of the eccentric means 24 in machines of the type illustrated be correlated with the direction of translation of the machine over the surface being compacted. That is, the eccentric will be rotated in one direction while the machine is moving forwardly and in the opposite direction while the machine is moving rearwardly. Unless this directional correlation is maintained, the roller 22 has a tendency to scuff and may mar some types of asphalt surfaces.

The resilient mount between the roller 22 and the frame 18 in a machine of the type illustrated is a relatively soft mount, and undesirable frame-to-roller resonance effects which might impose large stresses on the components may be avoided by quickly accelerating the eccentric means 24 through the critical range, as disclosed in the aforesaid Keppler patent. The eccentric speed which would cause roller-to-frame resonance is very much lower than that which would provide for maximum compaction efficiency. For example, the natural frequency of the vibrating system comprising the roller and the contacted ground surface portion ordinarily is three, five or even more times as great as the frequency at which frame-to-roller resonance could occur. At these higher levels the phase difference between the vibrations of the roller 22 and the frame 18 will approximate 180 at any of the eccentric speeds which might be dictated by the present invention.

The vibration of the roller 22 may be described as essentially a cyclical up-down movement. One cycle may be considered to embrace, when viewing the roller 22 from a stationary reference point at one end thereof, the movement of the roller from a maximum UlP position through a center or REST position to a maximum DOWN position and back through the REST position to the maximum UP position.

The cyclical movement of the eccentric means 24 may be considered, when viewing the eccentric means 24 from the same stationary reference point, to embrace the movement of the portion of the eccentric means displaced radially outermost of its axis of rotation (i.e., the eccentric portion) from a maximum UP position through a HORIZONTAL position to a maximum DOWN position and back through the HORIZONTAL position to the maximum UP" position.

The maximum UP and DOWN positions may be further defined as the points at which the vertical components of the velocity of the roller 22 are zero. The term REST position is used hereinafter in connection with any vibrating element may be defined as a reference point at which the verticalcomponent of velocity of the element is maximum and vertical component of acceleration is zero. It should be noted tha these reference positions, defined in this manner, are amplitude independent.

By reason of the mass of the compactor and the damping action of the surface being compacted, the cyclical movement of the roller 22 lags behind the induced cyclical movement of the eccentric means 24. For any given system, the amount of lag, or phase difference in movement, varies with the speed at which the eccentric means 24 is driven, i.e., its frequency of movement. When the speed or frequency of the eccentric means 24 equals the natural frequency of the vibrated system made up of the roller 22.and the ground portion contacted thereby, the system is at resonance and maximum compacting efficiency is achieved. In this condition, the amount of lag or phase difference between the movement of the eccentric means 24 and the roller 22 approximates the ideal phase difference of one-fourth of a cycle or 90. I

In actuality, this phase difference may vary from the ideal 90 condition and still achieve satisfactory compaction efficiency. For example, a phase difference of between 75 and 105 may be expected to produce good results. However, in instances wherein a detected phase difference below the desired predetermined range at which compacting efficiency is enhanced, e.g. where the difference is 70, the speed of the eccentric means 24 should be increased. When the detected phase difference is higher than that range, e.g. where the difference is 1 10, the speed of the eccentric means 24 should be decreased to achieve maximum compaction efficiency.

With continued reference to FIG. 1, it may be seen that provision is made for controlling the speed of the eccentric 24 either manually or automatically. A selector switch 34 is provided to permit the operator to select either automatic or manual control.

Manual speed control is accomplished by operator manipulation of a manual memory type speed control throttle 32. The throttle 32 is mechanically coupled through an eccentric means automatic direction control means 31, in any suitable manner as indicated at 33, to the pump 28 of the hydrostatic transmission which drives the eccentric means 24.

Additionally, a compactor propulsion control throttle 35 is mechanically connected to the direction control 31 to correlate the eccentric means rotational direction with the lateral direction of the compactor. Further details of this speed and direction control arrangement will be provided hereinafter in connection with FIG. 2 and also be found in the aforementioned Keppler disclosure.

Automatic speed control is accomplished pursuant to a detection of the phase relationship between the cyclical movement of the eccentric means 24 and the cyclical vibrational'movement of the roller 22. Following such detection a speed error signal is generated and applied to a speed adjustment motor 36 by way of the selector switch 34. This motor 36 is mechanically connected to the pump unit 28 of the hydrostatic transmission so that operation of the motor 36 in response to an error signal will produce an adjustment in the speed of the eccentric means. v

The speed error signal may also be applied to a conventional indicator 27,'such as a voltmeter, by way of a suitable electrical connection indicated at 29. The indicator may be calibrated to indicate whether the speed of the eccentric is above, at, or below the natural frequency of the vibrated system, and the operator may utilize these meter readings as bases for manipulation of the throttle 32 when the selector switch 34 is in its manual position.

The propulsion control throttle 35 for the machine and the eccentric speed control throttle 32 are pivotally mounted at appropriate locations on the tractor frame so that they may be manipulated conveniently by the machine operator. The movement of these throttle levers are in turn transmitted to the controlled components by means of flexible connectors such as bowden wires or cables. As is well known, cables are made up of a central wire and a surrounding sheath through which the central wire may be moved axially.

Two such wire-sheath connectors 37 and 43 are connected to the propulsion control throttle 35 in FIG. 2. One of these leads to the pump unit 15 of the hydrostatic transmission for driving the wheels 12 and 14 of the machine. Through suitable connections at the ends of this connector 37, a movement of the throttle lever 35 to the left of its full line position in FIG. 2 causes the machine to move over the ground in one direction and movement of the throttle lever 35 to the right of its full line position causes a reverse movement of the machine.

The other connector 43 connected to the propulsion throttle 35 leads to a switching mechanism 31, described in detail in the aforesaid Keppler patent to which reference may be made for a full explanation of the internal construction. It will be sufficient here to point out that this unit 31 responds to the position of the propulsion throttle 35 to correlate direction of eccentric rotation with direction of machine propulsion. A speed input to the unit 31 is indicated at 41 in the form of a lever, and a speed output lever is indicated at 42. Movement of the input lever 41 in one direction will cause different direction of movement of the output lever 42 depending upon the position of the throttle 35. These movements of the output lever 42 are in turn transmitted to the control input element of the unit 28 of the hydrostatic transmission for driving the eccentric means.

The position of the input lever 41 is controlled by a wire-sheath connector 39. The wire component of this connector 39 is attached to an end portion of the lever 41, and the adjacent end portion of the sheath component of the connector 39 is attached to a nut element 47 movable along a threaded portion 49 of the output shaft of a control motor 36. The opposite end of the connector 39 is coupled to the manually operable eccentric speed control throttle 32.

The construction of a preferred type of throttle is disclosed more fully in the aforesaid Keppler patent. This is a memory throttle which may be pivoted between "OFF and ON positions and which may be conditioned to produce different outputs when in its ON position by rotating a knob on the outer end of the throttle lever. The coupling between the throttle 32 and the connector 39 should be one which will assure that movement of the throttle lever 32 to its OFF position will move the input lever 41 of the unit 31 to its fully OFF" position under all conditions of adjustment of the nut 47 attached to the opposite end of the sheath of the connector. For example, since the lever 41 normally contactsa stop at its fully off position (the position at which the eccentric means is stationary), a stiff spring connection between the throttle 32 and the end of connector 39 will permit the throttle lever, in moving to its OFF' position, to pass in all instances the point required to position the lever 41 against its stop.

In addition, when the throttle 32 is in its full "ON position, as illustrated in phantom, the throttle handle is operative to close a conventional snap acting switch 51 secured to the tractor frame or throttle assembly in any suitable manner. The contacts of the switch 51 are electrically connected in series with the power to the motor 36 to permit the energization of the motor 36 only. when the throttle32 is in its ON position, as will hereinafter be described in connection. with FIG. 5.

With this arrangement, either the manually operable throttle 32 or the automatically controlled motor 36, or both, may exert speed controlling effects on the system. When the switch 34 is in its MANUAL position, the motor 36 will of course be inactive, and the throttle 32 is in full control of the eccentric speed.

When, however, the switch 34 is in its AUTO- MATIC position, both the throttle 32 and the motor 36 have roles to play. The motor 36 has no effect on eccentric speed until the throttle 32 is moved to its ON" position. Thereafter. the motor 36 assumes substantially complete command over the system because any speed changes dictated by rotating the knob at the end of the throttle lever 32 will quickly be corrected for by the motor 36. On the other hand, it is always possible to quickly stop the eccentric means in an emergency by simply moving the throttle 32 to its fully OFF position.

Moreover, this arrangement serves to screen from the area of automatic control those lower eccentric speed levels which might result in undesired roller-toframe resonance. By setting the knob on the throttle 32 to correspond with an eccentric speed well above the range of roller-to-frarne resonance, one can assure that the eccentric speed is increased beyond the danger level before actuation of the switch 51 upon arrival of the throttle at its ON" position enables operation of the control motor 36.

The relationship between roller 22, the eccentric means 24, the frame 18 and certain sensor components for the automatic control system will be explained with reference to FIG. 3, which illustrates one end portion of the vibrating roller and various parts associated therewith.

The vibration producingmeans or eccentric means 24iis mounted on a shaft 40 which extends coaxially through the roller 22. The shaft 40 also extends through a hollow hub 53 which is secured to two end plates 61 (only one of which is shown) of the roller 22. The shaft 40 is mounted within the hub 53 for rotation independently of the freely rotatable roller 22, for example, by means of suitable bearings 44. The shaft 40 is flexibly connected by a drive connection 46 to a shaft 55 upon which a rotatable sheave 48 is mounted. The shaft 55 upon which the sheave 48 is mounted may be rotatably supported by suitable bearings 50 within a hub 57 mounted on the roller support frame 18.

The sheave 48 is driven by the frame supported drive motor 26 of FIG. 1 by suitable flexible drive belts illustrated schematically in dotted lines in FIG. 1, at 52. Operation of the motor 26 thus causes rotation of the shaft 40 and the eccentric means 24 at a speed dependent upon the speed of motor operation. The resulting rotation of the shaft 40 and the eccentric means 24 develops forces which cause vibration of the resiliently mounted, independently rotatable roller 22.

An acceptable form of a resilient mounting for connecting the ground engaging compacting roller 22 to the frame 18 is illustrated in FIG. 3. The hub 53 connected to the end plate 61 of the roller 22 is journalled for rotation in a suitable bearing member 59 within a sleeve 56 extending through and being fixed to a beam 58. Resilient suspension members 60 flexibly connect the beam'58 to the frame 18 and permit limited relative motion between the roller 22 and the support frame 18.

For a more detailed description of the resilient mounting for the roller, as well as the flexible connection 46 between the sheave 48 and the eccentric shaft 40, reference may be had to US. Pat. No. 3,41 L420 (the disclosure of which is hereby incorporated by reference), assigned to the assignee of the present invention.

As previously noted, maximum compaction efficiency is achieved when the system operates at or near a resonant frequency determined, in part, by the characteristics of the surface or ground being compacted, and this resonance condition occurs when the movement of the eccentric means 24 leads the movement of the compacting roller 22 by a predetermined phase angle, i.e., when there is a phase difference in an acceptable range, centered about between the movement or instantaneous position of the eccentric means 24 and the movement or instantaneous position of the roller 22.

With continued reference to FIG. 3, the cyclical movement of the roller 22 may be detected photoelectrically by detecting the vertical position of the roller 22 relative to the frame 18 and generating a marker signal or pulse when a reference point on the roller 22 is aligned with a reference point on the frame 18 as the roller passes through the "REST position. To this end, a suitable, conventional lamp 62 may be mounted within a housing 64 to provide a narrow, directional light beam indicated at 66. The housing 64 may in turn be mounted on the frame 18 so that the light beam 66 is directed horizontally toward the roller 22. The lamp 62 may be operable, for example, to supply light when energized from a 12 volt d.c. source of power supplied via terminals 6% and 70 of a speed control unit hereinafter described in connection with FIG. 5.

The beam of light 66 from the lamp 62 is directed toward the roller support frame 18 and when the compactor is at rest, i.e., when there is no displacement between the roller 22 and the support frame 18 due to vibration forces, the light beam 66 may pass through a horizontally disposed slot 69 in a vertical member 71 mounted on the beam 58 to strike a light detector 72 mounted on a member 74 connected to the frame 18. The detector 72 is of a type which becomes substantially conductive only when impinged upon by the light beam 66 passing through the slot 69. A resilient housing generally indicated at 75 may enclose and thereby protect the lamp and detector assembly.

The cyclical movement of the eccentric means 24 may also be detected photoelectrically by detecting the angular position of the shaft 55 relative to the frame 18. A second lamp 80 within a housing 82 may be fixedly secured, in any suitable manner, to the frame 18. The lamp 80 may be identical to the lamp 62 and may be electrically connected in parallel therewith. A narrow, directional light beam 84 may be projected outwardly from the lamp 80 in a direction substantially perpendicular to an axially extending portion 86 of the sheave 48. A pair of diametrically opposed apertures 88 may be provided through the axially extending portion 86 of the sheave 48. When the eccentric means is in its HORIZONTAL" position the beam of light 84 passes through one of the apertures 88 and strikes a light detector 90 suitably mounted on the frame 18.

The light detector 90 may be identical to the light detector 72 previously described. The two leads of the light detector 90 are connected to two input terminals 92 and 94 of the speedcontrol unit 91 of FIG. 5.

The output signal from the detector 72 is related to the cyclical movement or vibrational position of the roller 22 and the output signal from the detector 90 is related to the cyclical movement or rotational position of the eccentric means 24. Therefore, the existence of resonance of the compacting roller may be detected by comparing the output signal from the light detector 72 with the output signal from the light detector 90 and generating a speed error signal if the phase difference between these output signals is other than a desired amount, i.e., 90, or alternatively, outside a desired range centered on the desired amount. To indicate whether the phase difference is greater or less than the desired amount, (and thus whether the speed or eccentric means should be increased or decreased), the polarity of the error signal may, for examplebe utilized.

In order to facilitate an understanding of the phase detection provided by the embodiment of FIG. 3, the relationship between the cyclical movement of the eccentric means 24 and the cyclical vibration of the roller 22, as well as the signals from the light detectors 72 and 90 is graphically illustrated in FIG. 4.

In FIG. 4, the waveform A is indicative of the vertical or up and down components of the movement of the eccentric 24. This movement may be represented by a sinusoidal wave which has a peak positive value when the eccentric means is in the UP" position and a peak negative when the eccentric means is in the DOWN" position. The sinusoidal wave has a zero value whenever the eccentric means is in the HORIZONTAL position previously described.

Waveform B illustrates the output signal from detector 90. Since light strikes the detector 90 whenever the eccentric means 24 is in the HORIZONTAL position, the output signal from the detector 90 is a series of positive voltage spikes which occur as the eccentric means 24 passes through the HORIZONTAL position.

Waveform C is indicative of the cyclical movement or vibration of the roller 22 when the ground compacting system is at resonance. The frequency of the sinusoidal wave of waveform C is the same as the frequency of the sinusoidal wave form A, i.e., the frequency of rotation of the eccentric means 24 is the same as the forced frequency of vibration of the roller 22. At resonance, the movement of the eccentric means 24 leads the movement of the roller 22 by 90 and therefore the waveforms A and C are 90 out of phase.

An output'signal is generated by the light detector 72 each time the roller vibration carries the slot 69 through the REST position illustrated in FIG. 3. Thus, waveform D, which illustrates the output signal or marker pulses from the detector 72, is a series of pulses occurring each time the roller 22 passes through the REST position.

When the phase relationship of FIG. 4 exists, no speed error signal is generated by the speed control unit 91 of FIG. 5. When phase relationships departing substantially from that of FIG. 4 exist, the speed control unit 91 is operative to control the frequency of the eccentric means 24 until the speed error signal is nulled or at least comes within acceptable limits. One embodiment of a speed controlunit 91 which may be utilized to generate the speed error signal in response tothe detected phase difference, as previously described, is schematically shown in detail in the functional block diagram of FIG. 5.

The speed control unit 91 may be mounted at any conventional location on the machine and may include a 12 volt d.c. or other suitable power supply 108, the positive and negative poles of which are connected, respectively, to terminals 68 and 70. The power supply 108 supplies electrical power to the lamps 62 and previously described and may additionally provide the electrical power required by the circuits hereinafter described.

The two output leads from the detector 72 are con nected to the terminals 76 and 78 of the speed control unit 91 which are in turn connected respectively to the positive terminal of the power supply 108 and through a current limiting resistor 112 to the reset input terminal R of a conventional bi-stable multivibrator or flipflop 110. The two leads from the detector are connected to the terminals 92 and 94 of the speed control unit 91 and the terminals 92 and 94 are connected respectively to the positive terminal of the power supply 108 and through a current limiting resistor 114 to the set input terminal S of the flipflop I10.

The binary ONE or Q output signal from the flip-flop 110 is applied through a conventional voltage averaging circuit 116'to one input terminal 118 of a conventional difference amplifier 120. A reference voltage, for example, a voltage taken from the arm of a potentiometer l 12 connected between the positive terminal of the power supply 108 and ground, is applied to the other input terminal 124 of the difference amplifier 120.

The magnitude and polarity of the output signal from the difference amplifier 120 represent, respectively. the amount and the direction of deviation of the detected phase difference between the movement of the eccentric means and the roller from a predetermined desired phase difference. The predetermined desired phase difference is determined by the value of the reference voltage applied to the input terminal 124 of the difference amplifier 120 as will be subsequently described in greater detail.

If a deadband is desired, i.e., a range of phase differences centered on the predetermined desired phase difference within which no speed error signal is generated by the speed control unit 91, the output signal from the difference amplifier 12 may be applied to any suitable conventional threshold circuit. For example, the output signal from the difference amplifier 120 may be applied to the anode electrode of a conventional semiconductor diode 121 and to the cathose electrode of an identical diode 122. The diodes 121 and 122 may be back biased by selectively variable voltages supplied, for example, from properly poled, ganged variable voltages d.c. power supplies 123 and 124, respectively. A control knob 125 is provided to manually vary the back bias applied to the diodes 121 and 122, and when the power supplies are set at a predetermined voltage, the output signal from the difference amplifier 120 must overcome this voltage (the back bias applied to the diodes) plus the forward drop across the conducting one of the diodes before an output signal will appear at a common connection or terminal 126 between the power supplies 123 and 124.

The output signal from the terminal 126 of the threshold circuit is applied to a conventional d.c. amplifier 127. The output signal from the amplifier 127 is applied through a contact 34a of the automatic/manual selector switch 34 of FIG. 1 and through a contact 51a of the snap acting switch 51 of FIG. 2 to one power input terminal of the conventional d.c. speed adjustment motor 36 of FIG. 2. Systemcommon or ground is provided at an output terminal 129 and the terminal 129 is connected through a contact 24b of the switch 34 to the other power input terminal of the motor 36.

In operation, a 12 volt d.c. level is applied to one lead of each of the light detectors 72 and 90 by way of terminals 76 and 92,respectively. When the beams of light from the respective lamps 62 and 80 strike the detectors 72 and 90 as previously discussed, the resultant decrease in the resistance of the detectors causes the generation of positive pulses as illustrated in FIG. 4.

The pulses from one of the detectors, for example, the detector 90, set the flipfiop 1 10,and the pulses from the other detector 72 reset the flipflop 110. When the pulses from the detector 90 are displaced from the pulses from the detector 72 by a phase magnitude corresponding to one indicative of resonance of the compacting roller, the output signal from the flipflop 110 is a rectangular waveform comprising pulses having a predetermined amplitude, e.g. 6 volts, and a duration equal to one-half of one complete cycle of the rectangular waveform. Thus, at system resonance the ON" time of the pulses from the flipflop is exactly equal to the OFF time thereof and the average value of the series of pulses is one-half the maximum amplitude of the individual pulses, i.e., 3 volts. By applying a 3 volt signal to the difference amplifier from the potentiometer 122, the 3 volt average signal from the averaging circuit 116 is cancelled and the output signal from the difference amplifier 120 is zero volts. However, when the ratio between the ON and OFP times of the series of pulses from the flipflop 110 is greater or less than one, the average value of the pulses will be greater or less than 3 volts and the output signal from the difference amplifier 120 will be a positive or negative d.c. voltage.

The polarity of the output signal from the difference amplifier 120 is related to the direction in which the detected phase difference deviates from the predetermined desired phase difference. The magnitude of the output signal from the difference amplifier 120 is related to the amount of deviation of the detected phase difference fromthe predetermined desired phase difference.

When the automatic/manual switch is in the automatic position, and when the control throttle 32 is in the ON" position, this output signal may be applied directly to the d.c. amplifier 127 to energize the motor 36 and vary the speed of the eccentric means. Direct application of this signal to the motor 36 through the d.c. amplifier 127 causes the motor 36 to vary the speed of the eccentric means until the predetermined desired phase difference is achieved.

However, the output signal from the difference amplifier 120 is preferably applied to the d.c. amplifier 127 through a threshold circuit as previously described. By varying the threshold value of the threshold circuit, i.e., by varying the magnitude of the back bias applied to the diodes 121 and 122, a deadband is provided.

Thus, the magnitude of the output signal from the difference amplifier 120 (and therefore the amount of deviation of the detected phase difference from the predetermined desired phase difference) must exceed this threshold value before speed corrections are made.

For example, if the output signal from the difference amplifier 120 is positive, the positive polarity indicates that the phase difference between the movement of the eccentric means 24 and the roller 22 vibration is greater than the predetermined desired phase difference. If the amplitude of this signal exceeds the threshold value, the speed of the eccentric means 24 is reduced. Likewise, a negative error signal from the difference amplifier 120 of sufficient amplitude to overcome the threshold value would indicate that the phase difference between the movement of the eccentric means 24 and the vibration of the roller 22 is outside the lower limit of the deadband range, requiring an increase in eccentric means speed.

The potentiometer 122 need not be set at a value which locks" the system at the ideal resonance condition of 90 phase difference. If desired, the operator may adjust the potentiometer to provide predetermine desired phase relationships other than 90 or dead bands centered about predetermined desired phase relationships other than 90. For example, by adjusting the potentiometer 122 to apply a slightly lower voltage to the difference amplifier, the system would then operate with a phase difference of less than 90 between the movement of the eccentric means 24 and the vibration of the roller 22, e.g. at 85, or with the deadband centered at this lower phase difference.

Another manner in which the phase relationship between the cyclical movement of the eccentric means 24 and the cyclical vibration of the roller 22 may be determined and controlled is illustrated in FIG. 6.

In the embodiment of FIG. 6, the detection of the cy clical vibrational movement of the roller 22 and generation of marker pulses is accomplished through the use of a lamp 62 and a detector 72 in a manner identical to that previously described in connection with FIG. 5. The lamp 80 mounted on a suitable support 130 secured to the support frame 18 and the detector 90 mounted on a suitable support 131 secured to the frame 18 are also provided to detect the movement of the eccentric means, as discussed in connection with FIG. 5.

However, the embodiment of FIG. 6 maintains the phase relationship between the movement of the eccentric means 24 and the roller 22 within a desired range, Le, a deadband", by providing additional eccentric means movement or position detectors.

In the FIG. 6 embodiment, a lamp 132 within a housing 134 is mounted adjacent the lamp 811 on the support 130. The lamp 132 provides narrow, directional light beams 136 and 138 which are directed, respectively, radially outwardly toward the axial extension of the sheave 48 and axially outwardly toward an axially facing and radially inwardly extending arcuate member 140 attached to the interior surface of the axial extension of the sheave 48.

A second conventional light detector 142 is mounted adjacent the light detector 90 on the support 131. Slots the openings or apertures is thus preferably such that the projections into the same plane of lines extending from the axis of the shaft 55 to the apertures 144 and 146 define a 30 angle, as indicated at 1 0 in F IG. 7.

As indicated by the arrow 48a in FIG. 7, the sheave 48 which drives the eccentric means 24 is rotating, for example, in a clockwise direction. As the sheave 48 rotates it will be appreciated that the light detector 90 is energized prior to the energization of the light detector 142 by reason of the predetermined orientation of the apertures 144 and 146. The light detector 148 lies in the same plane as the light detectors 90 and 142 and is energized throughout most of each revolution of the sheave'48. However, the detector 148 is de-energized shortly after the apertures 144 and 146 have been rotated beyond the plane of the detectors when the radi- 144 and 146 (FIG. 7) are provided through the axial I extension of the sheave 48. When these openings are aligned with the light beams 84'and. 136, respectively, the light beams strike the respective light detectors 90 and 142. As will be described in connection with FIG. 7, the openings 144 and 146 are positioned so that the signals from the detectors 90 and 142 provide information as to two different positions of the eccentric means 24.

A third conventional light detector 148 is provided on the support 130. The detector 148 is positioned so that the light beam 138 strikes the detector as the sheave 48 rotates, except for a portion of each cycle during which the arcuate member 140 is interposed between the lamp 132 and the detector 148. The detector 148 then provides a "chopping signal which is utilized by the speed control unit as will hereinafter be described.

The relative angular positions of the apertures 144 and 146, the arcuate member 140, and the detectors 90, 142 and 148 are illustrated schematically in FIG. 7 for clarity. The position of the eccentric means 24 mounted on the shaft is superimposed on FIG. 7 in phantom to show the position of the eccentric means 24 as related to that of the sheave 48.

As will be evident, the openings 144 and 146 are displaced from each other by a predetermined angle. Since compaction efficiency ordinarily may be maximized when the phase difference between roller and eccentric means movement is 90:tl5 (75 to 105), the predetermined amount of displacement between ally extending arcuate member 140 blocks the light beam 138, shown in FIG. 6. The web 132 thus provides a chopping action which resets the speed control unit once during each revolution of the eccentric means 24, as will hereinafter be described.

The relationship between the movement of the eccentric means 24 and the vibration of the roller 22 at resonance, and the resultant output signals from the detectors 72, 90, 142, and 148 are shown for one complete cycle of 360 in FIG. 8 as the respective waveforms A, B, C, D, E, and F. Due to the relative positions of the detectors and 142 and the apertures 144 and 146, the signal from the detector 90 (waveform D) is generated when the eccentric means 24 is moving upwardly and is displaced more than 15 from the maximum UP position, and the signal from detector 142 (waveform F) is generatedwhen the eccentric means 24 is moving downwardly and is displaced more than 15 from the maximum UP" position. Also, due to the relative positions of the detector 148 and the arcuate member 140, the signal from the detector 148 (waveform E) is chopped" or interrupted shortly after both detectors 90 and 142 have been energized. The signals from the detectors 72, 90, 148 and 142 (shown, respectively, as waveforms C, D, E, and F of FIG. 8) are utilized by the speed control unit to generate motor speed control signals which may be applied to the auto/manual selector switch 34 previously described in connection with FIG. 5. A speed control unit 152 suitable for use with the embodiment of FIG. 6 is shown in FIG. 9.

Referring now to FIG. 9, the lamps 62, 80 and may be supplied with power from a suitable source of d.c. potential such as a battery 154. The two leads from the detector 72 may be connected, respectively, to the positive terminal of the battery 154 and to one of the leads from each of the detectors 0 and 142.

The other lead from the detector 90 is connected through a suitable current limiting resistor 155 to the trigger or gate electrode of a silicon controlled rectifier (SCR) 156. The other lead from the detector 142 is connected through a suitable current limiting resistor 157 to the trigger or gate electrode of a second SCR 158.

One lead from the detector 148 is connected to the positive terminal of the battery 154 and the other lead from the detector 148 is connected to the anode electrode of the SCR 158 which is in turn connected directly to the anode electrode of the SCR 156. The speed error signals from the speed control unit 152 are obtained from the cathode electrodes of the SCRs 158 and 156 which are connected, respectively, to the contacts 34a and 34b of the automatic/manual selector switch 34. With the switch 34 in the automatic position, these speed error signals are applied through the contacts 51a and 51b of the snap acting switch 51 of FIG. 2 to the speed adjustment motor 36 previously described.

In operation, the output signal or marker pulse 8 from the light detector 72 enables the light detectors 90 and 142 each time the roller 22 passes through the REST position. If the position of the eccentric means 24 is such that light strikes the detector 90 while it is enabled, the SCR 156 is triggered and an output signal is applied to the speed adjustment motor via the switch contacts 34b and 51b. Since this output signal from the SCR 156 indicates that the phase difference between the movement of the roller 22 and the movement of the eccentric means 24 is less than 90, e.g., 75 or less, the output signal from the SCR 156 causes the speed adjustment motor 36 to increase the speed of the eccentric means 24. A short time later, the SCR 156 is turned off when the signal from the detector 148 is chopped or interrupted thus interrupting the current flow through the SCR 156. The system is thereafter ready for subsequent position or movement detection, i.e., detection on the next cycle.

On the otherhand, if light strikes the detector 142 when an enabling marker signal from the detector 72 is present, the .SCR 158 is triggered and provides a speed control signal which is applied to the motor 36 through the switch contacts 34a and 51a. Since the output signal from the SCR 158 indicates that the phase difference is greater than 90, e.g., 105 or more, the output signal from the SCR 158 causes the speed adjustment motor 36 to decrease the speed of the eccentric means 24. Again, the SCR 158 will be turned off when the power applied to the SCR is chopped or interrupted and the circuit is reset for detection during the next cycle.

Thus, with the speed control system described in connection with FIGS. 6 through 9, the phase difference between the movement of the roller. 22 and the eccentric means 24 may be kept within desired tolerances such as the 75 to 105 tolerances previously described. Since there is a "deadband" between the 75 phase difference and the 105 phase difference within which there can be no coincidence between the marker pulse and the signals from the detectors 90 and 142, any phase difference variations falling within the deadband" will not cause the system to generate speed error signals.

This system also may be provided with a meter 27a for indicating visually, at a location convenient to the machine operator. whether the phase difference between the roller and the eccentric is below, at or above the deadband. With this type of meter, the pointercenters when the eccentric roller phasedifference is in the deadband. swings in one direction when this phase difference is below the deadband, and swings in the opposite direction when the phase difference is above the deadband.

While lamps and appropriately placed light detectors may be utilized to detect the movement of the roller 22 and the movement of the eccentric means 24 as previously described, the movement of the eccentric means 24 and of the roller 22 may be detected by appropriate cams and switches and electromagnetically, respectively, as illustrated in FIGS. 10 and 12.

With reference now to FIG. 10, it will be noted that the movement of the eccentric means 24 may be detected by appropriate cams 160, 162 and 163 mounted on a rotatable shaft 164 which is driven in synchronism with the eccentric means 24 and which may be an extension of the sheave axle. A suitable spring biased cam follower 166 rides on the cam and opens a set of normally closed switch contacts 168 when driven outwardly by the cam 160. Spring biased cam followers 170 and 172 ride on the surfaces of cams 162 and 163 and likewise open a set of normally closed switch contacts illustrated schematically at 174 and 176, respectively, when driven outwardly by the cams 162 and 163.

The switch contacts 168, 174 and 176 may be mounted within suitable housings as illustrated and the housingsmay be fixedly mounted in a suitable manner on support members 169 which are in turn connected to a housing 171. The housing 171 may be connected to the frame 18 of the compactor as illustrated to suitable support for the assembly.

The shapes of the cams 160, 162 and 163, and the position of the cam followers 166, 170 and 172 are such that the switch contacts 168, 174 and 176 open and close in accordance with the diagram of FIG. 11. CAm and switch arrangements of this type are well known in the art and will, therefore, not be described in detail.

In FIG. 11, the curve A illustrates the cyclical movement of the eccentric means 24 as it is driven through one revolution. The curve B illustrates the position of the switch contacts 168. It can be seen that the switch 168 is open during a short portion of, each revolution, e.g. when the eccentric means is in the DOWN" position to provide chopping" action. Curve C illustrates the position of the contacts of the switch 174. As illustrated, the contacts of the switch 174 are closed, for example, about a 60 portion of the 360 revolution of the eccentric means 24. This 60 portion starts approximately 75 before the eccentric means reaches the UP position and thus ends about 15 before the eccentric means reaches the UP position.

The position of the contacts of the switch 176 is shown as curve D.-As illustrated, the contacts close about 15 after the eccentric means has rotated through the UP position and remain closed for about a 60 portion of one revolution of the eccentric means.

An appropriate electromagnetic detector such as that illustrated in FIG. 12 may be utilized to detect the vibration of the roller 22 and to generate a marker pulse when the roller vibrates through the REST" position.

In FIG. 12, a magnet 180- is illustrated as being mounted on the beam 58 which, it will be remembered, vibrates with the roller 22. The magnet 180 is provided with two arms 182 and 184 extending outwardly toward the frame 18 and having an air gap between the outermost ends thereof. A coil of wire 186 is mounted on the frame 18 and is positioned so that the coils are in the air gap intermediate the arms 182 and 184 when the roller 22 is in the rest position. Each time the roller 22 vibrates through the rest position, an electrical marker pulse is generated by the coil 186. For example, the coil may be wound so that a positive pulse is generated as the roller vibrates upwardly through the rest position.

The marker" pulse generated by the coil 186 may be utilized by a suitable speed control unit in lieu of the marker pulse from the light detector 72 of FIGS. and 9, and the switches 168, 174 and 176 may be employed in lieu of the light responsive means heretofore described for providing inputs to the speed control unit. Alternatively, these features may be combined in a single system.

The electrical connection of the contacts of the switches 168, 174 and 176 of FIG. and the coil 186 of FIG. 12 to a suitable speed control unit is illustrated in FIG. 13 which depicts a speed control unit identical to the speed control unit 152 of FIG. 9. Therefore, only the connection of the switches and the coil of the embodiments of FIGS. 10 and 12 of the speed control unit need be described.

One end of the coil 186 is connected to system common or ground and the other end thereof is connected through a conventional semiconductor diode 188 to one contact of each of the switches 174 and 176. The diode 188 is poled to pass only positive pulses from the coil 186 to the contacts of the switches. Additionally, a suitable zener diode 190 may be connected between the cathode electrode of the diode 188 and ground to limit the amplitude of the signal generated by the coil 186.

Another technique which may be uitlized to detect the movement of the roller'22 and the movement of the eccentric means 24 and to relate these detected movements to provide speed control signals, is illustrated schematically in FIG. 14.

In this embodiment, a generally U-shaped magnet 200, the legs of which are generally horizontal and are separated by an air gap 202, is mounted on a bracket 204 for pivotal movement about an axis generally indicated at 206. The bracket 204 is mounted on the vibratory compactor so that while it does not rotate with the roller, it cyclically vibrates therewith. For example, the bracket 204 may be mounted on the beam 58, as illustrated. with the pivot axis 206 perpencidular to the axis of the roller 22.

A spring 208 biases the magnet 200 to a predetermined position and a coil of wire 210 is mounted on the bracket 204 by suitable means 212 so that only the top of the coil lies within the air gap 202 as illustrated.

The pivoted magnet 200 and the spring 208 together form a mechanical oscillator. As the roller vibrates, the magnet 200 is forced to vibrate generally up and down as indicated by the arrows at 205. Themass of the magnet 200 and the resiliency of the spring 208 are chosen so that the resonant frequency of the mechanical oscillator is less than one-third the lowest resonant frequency (of the vibratory compacting system) normally encountered when compacting various surfaces. Thus, when the vibratory compacting system is operating at or near resonance, its vibrational frequency will be at least three times that of the magnet and the up-down movement of the magnet 200 will be approximaTely 180 out of phase with the movement of the roller 22.

The coil 210 is wound so that the signal generated at an end 214 thereof is positive with respect to an end 216 as the magnet passes through the rest or bias position in the downward direction. This, of course, corresponds to movemnt of the roller 22 in the upward direction.

The magnet 200 is so constructed that a strong. narrow magnetic field is provided in the air gap 202 between the legs thereof. The width of the "marker" pulse generated by the cutting of this magnetic field by the coil of wire 210 as the magnet vibrates is directly related to the velocity at which the field is cut by the coil 210 and to the width of the field (which is constant). Since the velocity of the magnet 200 as it passes through the REST position is directly related to the frequency of vibration of the roller 22, the width of the marker" pulse is directly related to the frequency of vibration of the roller 22.

The resonant frequency of the roller-ground system varies with surface compaction, i.e., the resonant frequency increases as surface compaction increases. When compacting relatively loose surfaces, the band of vibration frequencies over which beneficial rollerground resonance effects occur is somewhat large. On the other hand, when compacting relatively hard surfaces, the frequency of vibration of the roller must be kept within much closer tolerance with respect to the natural frequency. Thus, this variation of marker pulse width with frequency of vibration is consistant with the need for greater accuracy at higher system natural frequencies.

This marker" pulse' may be used in connection with the signals related to the movement of the eccentric means 24, obtained as previously described, to generate speed error signals. Alternatively, the movement of the eccentric means 24 may be detected in the manner illustrated in FIG. 15.

Referring now to FIG. 15, an electrically nonconductive cylinder 218 is connected to the eccentric means drive, e.g. the sheave 48, and rotates at the same speed as the eccentric means 24. The cylinder 218, together with a brush 220 and a pair of brushes 222 and 224, provide a means for detecting the movement of the eccentric means 24.

The cylinder 218 is provided with an electrically conductive peripheral portion 226 to which is connected an electrically conductive, axially extending, arcuate portion 228 having an angular extent less than the angular spacing between the branches 222 and 224. The brush 220 is in wiping engagement with the conductive peripheral portion 226 of the cylinder 218 at all times. The brushes 222 and 224 are axially displaced from the brush 220 as illustrated so that the brushes 222 and 224 engage the axially extending arcuate portion 228 of the cylinder during only a portion of each revolution of the eccentric means 24. Further, the arcuate portion 228 is positioned so that it assumes the position illustrated in FIG. 15, Le, it is centered between the brushes 222 and 224, when the eccentric means is in the UP positron.

The cylinder 218 rotates with the eccentric means 24, for example, in the direction illustrated by the arrow 230. The radial position of the brush 222 is such that the conductive arcuate portion 228 of the cylinder 218 provides an electrically conductive path between the brush 222 and the brush 220 when the eccentric means 24 is displaced a predetermined amount in one direction from the UP position. The radial position of the brush 224 is such that a conductive path is provided by the conductive arcuate portion 228 of the cylinder 218 when the eccentric means is displaced a predetermined amount in the other direction from the UP" position.

A suitable speed control unit for generating appropriate speed control signals utilizing the detectors of FIGS. 14 and 15 is shown in FIG. 16.

Referring to FIG. 16, the marker pulse from the end 214 of the coil 210 is applied through a suitable semiconductor diode 234, poled to pass positive pulses from the coil, and through a current limiting resistor 236 to the brush 220. An amplitude limiting zener diode 238 may be utilized as previously described. The other end 216 of the coil 210 is connected to system ground or common.

The brush 222 is connected to the trigger or gate electrode of an SCR 240 and the brush 224 is connected to the gate electrode of an SCR 242. The cathode electrodes of the SCRs 240and 242 may be connected to the respective contacts 34b and 34a of the automatic/manual selector switch 34. The anode electrodes of the SCRs may be connected together and are connected through a suitable chopper, such as the eccentric means driven chopper switch contacts 168 of P16. 10, to the positive terminal of a suitable dc. power supply.

The arrangement of FIGS. 14-16 thus provides an.

automatic speed control which keeps the phase difference within a desired deadband" range centered on 90. Also, it should be noted that the effects of changes in the relative positions of the frame 18 and the roller 22 due to changes in loading of the resilient mounting does not affect the accuracy of this system.

It should be further noted that the previously described systems may be utilized to provide eccentric means speed control when the eccentric means is rotating in either direction by reversing the leads which supply the information as to the position of the eccentric means in response to a reversal of the direction of rotation of the eccentric means. This may be accomplished by providing appropriate switch contacts (for example, as illustrated in phantom at 250 in FIGS. 9, l3, and 16) between the eccentric means position detectors and the speed control unit. These switches may, for example, be operative to reverse the leads supplying the above information in response to the movement of the propulsion throttle 35 of FIG. 2.

Still other modes of utilization of the invention are feasibleJFor example, although the transducer shown in FIG. 14 has been described as mounted for vibration with the roller 22,.it is feasible to position an identical transducer 192 on the frame 18 as indicated diagrammatically in FIG. 1. The frame is forced by the roller to vibrate with detectable amplitude, and, at all eccentric speeds high enough to be of interest here, there is about a 180 phase difference between the vibration of the roller and the vibration of the frame. Consequently, the transducer 192 will provide an output signal which is related to the vibration of the roller 22 even though it is attached to the frame 18.

When the roller is in the maximum UP" position, the frame can be considered to be in the maximum DOWN" position. As the roller and frame vibrate at substantially the same frequency, both the roller and frame pass through the point of zero acceleration (i.e. the "REST" position) almost simultaneously. Thus, when it is desired to generate a marker" pulse when the roller vibrates through the REST" position, a marker" pulse may instead be generated by the transducer 192 sensing the frame passing .through the REST" or zero acceleration position.

The output signal from the transducer 192 may be applied to the speed control unit 1520f FIG. 13 in lieu of the signal-from the coil 186.

The resultant marker pulse is there compared to a signal related to the cyclic movement of the eccentric means 24 obtained, for example, in a manner such as that previously described in connection with the embodiments of FIGS. 5, 9, or 13 to generate appropriate speed error signals.

The invention kay be embodied in still other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed is:

1. IN a ground compacting machine of the type which includes an operators station; vibration producing means cylically movable at selectively variable frequencies; and means including a ground contacting member vibrated by said vibration producing means; the improvement comprising:

means on the machine responsive to the phases of said vibration producing means and said means vibrated thereby for producing a signal output independently of the relative vibration amplitude of the vibration producing means and the means vibrated thereby, the signal output being related solely to a phase difference; and,

means on the machine adjacent said operators station and operatively connected to said responsive means for producing a visual indication from said output.

2. A ground compacting machine according to claim 1 including means responsive to said signal output for regulating :the frequency of said vibration producing means.

3. In a vibratory compactorof the type including a frame, a ground engaging compacting member resiliently mountedon the frame, and vibration producing means cyclically movable at selectively variable frequencies for cyclically vibrating the compacting member at substantially the cyclic frequency of the vibration producing means to cause the compacting member to engage the ground in compacting relationship, the improvement comprising:

first detector means for detecting the cyclic movement of the vibration producing means;

second detector means for detecting the cyclic movement of the compacting member;

means responsive to said first and second detector means for determining, independently of the relative amplitudes of the detected cyclic movements, the relationship of a predetermined phase difference desired to be maintained during operation of the machine to the existing phase difference between the detected cyclic movement of the vibration producing means and the detected cyclic movement of the compacting member; and

means for varying the frequency of said vibration producing means, whereby such frequency may be adjusted to produce the desired correlation of the phase difference between the cyclic movements of the vibration producing means and the compacting 

1. IN a ground compacting machine of the type which includes an Operator''s station; vibration producing means cylically movable at selectively variable frequencies; and means including a ground contacting member vibrated by said vibration producing means; the improvement comprising: means on the machine responsive to the phases of said vibration producing means and said means vibrated thereby for producing a signal output independently of the relative vibration amplitude of the vibration producing means and the means vibrated thereby, the signal output being related solely to a phase difference; and, means on the machine adjacent said operator''s station and operatively connected to said responsive means for producing a visual indication from said output.
 2. A ground compacting machine according to claim 1 including means responsive to said signal output for regulating the frequency of said vibration producing means.
 3. In a vibratory compactor of the type including a frame, a ground engaging compacting member resiliently mounted on the frame, and vibration producing means cyclically movable at selectively variable frequencies for cyclically vibrating the compacting member at substantially the cyclic frequency of the vibration producing means to cause the compacting member to engage the ground in compacting relationship, the improvement comprising: first detector means for detecting the cyclic movement of the vibration producing means; second detector means for detecting the cyclic movement of the compacting member; means responsive to said first and second detector means for determining, independently of the relative amplitudes of the detected cyclic movements, the relationship of a predetermined phase difference desired to be maintained during operation of the machine to the existing phase difference between the detected cyclic movement of the vibration producing means and the detected cyclic movement of the compacting member; and means for varying the frequency of said vibration producing means, whereby such frequency may be adjusted to produce the desired correlation of the phase difference between the cyclic movements of the vibration producing means and the compacting member with said predetermined phase difference.
 4. A vibratory compactor according to claim 3, including means for establishing as said predetermined phase difference a lag of said compacting member about 90* behind said vibration producing means.
 5. A vibratory compactor according to claim 4, including means for controlling said frequency varying means in response to the output from said phase difference relationship determining means to effect an increase in the frequency of said vibration producing means when said compacting member lags behind said vibration producing means less than said predetermined frequency difference and to effect a decrease in the frequency of said vibration producing means when said compacting member lags behind said vibration producing means more than said predetermined frequency difference.
 6. A vibratory compactor according to claim 3, wherein said first detector means comprises means for detecting at least one cyclic position of the vibration producing means relative to the frame; and, wherein said second detector means comprises means carried by the frame for detecting at least one cyclic position of the frame, the cyclic position of the frame being related to the cyclic position of the compacting member.
 7. A vibratory compactor according to claim 3, wherein said first detector means comprises means for detecting at least one cyclic position of the vibration producing means relative to the frame in response to the position of a reference on the vibration producing means relative to the position of a reference on the frame; and, wherein said second detector means comprises means for detecting at least one cyclic position of the compacting member relative to the frame in response to the position of a reference on the compacting member relative to the position of a Reference on the frame.
 8. A vibratory compactor according to claim 7, wherein said second detector means includes light beam producing means and photosensitive means, one of such means being mounted for movement with said compacting member and the other being mounted for movement with said frame at a position such that the light beam contacts said photosensitive means when the relative movement between the compacting member and the frame brings these parts to the relative vertical locations occupied thereby when the machine is at rest.
 9. A vibratory compactor according to claim 7, wherein said second detector means includes magnetic field generating means and electric conductor means, one of such means being mounted for movement with said compacting member and the other being mounted for movement with said frame at a position such that said electric conductor means cuts said magnetic field when the relative movement between the compacting member and the frame brings these parts to the relative vertical locations occupied thereby when the machine is at rest.
 10. A vibratory compactor according to claim 3, wherein said second detector means comprises means for detecting at least one cyclic position of the compacting member at which the vertical component of acceleration of said member is about zero.
 11. A vibratory compactor according to claim 10, wherein said second detector means includes a mass mounted for vibration relative to said compacting member in a vertical direction at substantially the same frequency, and means for generating a marker pulse each time said mass moves in one direction past a center point of its path of vibrating movement.
 12. A vibratory compactor according to claim 11, wherein said mass is supported on said compacting member.
 13. A vibratory compactor according to claim 12, including magnetic field generating means and electric conductor means, one of such means being mounted for movement with said mass and the other being mounted for movement with said compacting member, said conductor means being positioned to cut said magnetic field as said mass moves past a center point of its path of vibrating movement.
 14. A vibratory compactor according to claim 11, wherein said mass is supportd on said frame and the cyclic position of said frame is related to the cyclic position of said compacting member.
 15. A vibratory compactor according to claim 14, including magnetic field generating means and electric conductor means, one of such means being mounted for movement with said mass and the other being mounted for movement with said frame, said conductor means being positioned to cut said magnetic field as said mass moves past a center point of its path of vibrating movement.
 16. In a compactor of the vibratory roller type which includes a frame, rotatable shaft means, means including a resilient element for connecting said shaft means to said frame for rotation and bodily movement relative thereto, an eccentric mass fixed on said shaft means for rotation therewith, a ground contacting compaction roller mounted for free rotation on said shaft means and variable speed drive means for rotating said shaft means to rotate said eccentric mass and produce vibration of said roller relative to said frame, the improvement which comprises: means for producing a first signal when said eccentric mass passes a certain portion of its path of movement and for producing a second signal when said roller passes a certain point in its path of vibrational movement; means responsive to said first and second signals for producing a signal output related to the angular difference between the occurrences of said first and second signals, said signal output being produced by said responsive means independently of the relative amplitudes of said first and second signals.
 17. A compactor according to claim 16, including means for automatically adjusting said variable speed drive means to change the speed of said eccentric mass in one diRection when said angular difference is below a predetermined value and to change the eed of said eccentric mass in the opposite direction when said angular difference is above a predetermined value.
 18. A compactor according to claim 16, including means for producing a third signal when said eccentric means passes another point in its path of movemnt; and means responsive to said second and third signals for producing a second signal output related to the angular difference between the occurrences of said second and third signals.
 19. A compactor according to claim 18, wherein said third signal trails said first signal by a predetermined angle in the direction of rotation of said eccentric mass, and wherein means responsive to said signal outputs is provided for automatically aadjusting said variable speed drive means to increase the speed of said eccentric mass when said second signal trails said first signal and for decreasing the speed of said eccentric mass when said second signal leads said third signal.
 20. A compactor according to claim 16, wherein said shaft means includes a first shaft element mounted on said frame for rotation about an axis fixed with respect to said frame, a second shaft element coaxial with said compaction roller, and means rotatably coupling said shaft elements together while permitting bodily movement of said second shaft element relative to said frame; and wherein said means for producing said first signal includes means for generating a signal in response to the roation of an angular segment of said first shaft element past a reference station fixed with respect to said frame.
 21. A compactor according to claim 20, wherein said means for generating a signal in response to the rotation of an angular segment of said first shaft element past a reference station fixed with respect to said frame includes an annular member fixed coaxially to said first shaft element and having an opening therethough; and light source means and photosensitive means fixed to said frame in positions such that light from said source means strikes said photosensitive means when said opening is located between said source means and said photosensitive means.
 22. A compactor according to claim 20, wherein said means for generating a signal in response to the rotation of an angular segment of said first shaft element past a reference station fixed with respect to said frame includes cam and cam follower means carried respectively by said first shaft element and said frame; and switch means actuated by said cam follower means.
 23. A compactor according to claim 20, wherein said means for generating a signal in response to the rotation of an angular segment of said first shaft element past a reference station fixed with respect to said frame includes cylindrical means rotatable with said first shaft element and having an electrically conductive surface portion; and brush means mounted on said frame in position to contact said electrically conductive surface portion during a portion of each revolution of said first shaft element. 